This invention relates to a railroad car dumping apparatus and to an improved weight sensing assembly associated therewith. Railroad cars handling large quantities of bulk materials are unloaded rapidly by inverting one or more of the railroad cars bodily to discharge the contents into a suitable hopper for further handling. It is desirable in such car dumpers to weigh the bulk material prior to dumping. There are generally provided in such dumpers weighing devices such as load cells placed in compression by the weight of the car, its contents, and any supporting structure above the load cell. Early attempts at designing a weighing means associated with car dumping apparatus resulted in an arrangement where substantially the entire car dumper was weighed and the weighing device was calibrated to subtract the structural members and the weight of the car from the total weight so that only the contents of the car were weighed. However, the weight of the contents is a very small percentage of the total weight and the margin for error was large.
A solution to that problem is disclosed in U.S. Pat. No. 2,896,935, wherein there is provided a cradle, a railroad car carrier apparatus invertible therewith, including a scale platform having rails thereon, and weight sensing apparatus coacting between the carrier and the scale platform. Because of the structure of such a device, the connection between the carrier and the platform includes the weight sensing device and is fabricated to operate both in compression, whereby the weight is sensed, and in tension when the apparatus is in its inverted car discharging position but without a railroad car on the rails.
An improvement in that arrangement may be found in U.S. Pat. No. 3,602,324, wherein the structure is considerably simplified by providing a platform assembly which is invertible with the cradle, but which does not require the provision of a separate carrier of which the scale platform is a part, nor does it require means for joining the scale platform and the carrier through the weight sensing apparatus whereby the latter must operate both in compression and in tension. Load cells or weight sensing devices remain more accurate when operated in compression only and not submitted to tensile stress.
A further desirable feature in a car dumper is the ability of the car carrying platen to shift to one side of the cradle during inversion so that cars having varying widths may be carried by the cradle and securely clamped in place. Such a shiftable table is shown in U.S. Pat. No. 2,896,935. However, in that patent, the load cells necessarily shift with the table, since they are located between the carrier and the scale platform. Thus, in addition to the tensile loads placed on the load cells, those load cells are subjected to lateral forces as the carrier shifts on the rollers. Furthermore, flexible leads must be provided on the load cells to accommodate the shifting movement of the carrier and those leads are subjected to mechanical wear and abrasion. A similar arrangement is shown in U.S. Pat. No. 3,373,829, wherein the load cells are provided between the weighing platform and the wheels. A further disadvantage in the structure of that patent is the fact that the weight of the car is sensed by the load cells through flexure of the structural members of the shiftable carriage.